Much to our surprise and pleasure, my wife Helen and I found ourselves enjoying a spot of lunch with Nigel Melville last weekend. A scrum-half of the highest calibre, a successful coach at Premiership level and a friend of long standing, it was good to see him back in the North of England. Nigel does not surface in this neck of the woods often, thanks to the demands of his job as chief executive of USA Rugby, a role he has been performing for six years.

My mind goes back to 1984, when he made his England debut, as captain, against a great Wallaby side boasting the likes of David Campese, Michael Lynagh, Mark Ella and Nick Farr-Jones – the youngest player to do so at that point in our rugby history. Largely because of injury, his international career was intermittent and lasted only four years. Summoned to New Zealand by the Lions as an uncapped player in '83, he was hurt in his second game and played no further part. It was a sign of things to come, sadly. His bad luck on the fitness front continued and forced him into premature retirement.

I was a scrum-half too, back in the dim and distant past, so it was inevitable that our talk of sport and life in general eventually narrowed down to a discussion about No 9s and their role in the game we love. I coached Nigel between '84 and '86, both with the North of England team and the full national side and it was a privilege to do so, for he was renowned throughout the union world for the speed and accuracy of his service, particularly off the floor. That pass of his bought an inordinate amount of time for his stand-off.

Passing was his bread and butter, his raison d'être: his wonderful technique allowed him to create and maintain a consistent and well-oiled link between the hard-working coalface merchants in the tight five and the runners in the outside backs. Slow ball was not on the agenda when Nigel played, and colleagues venturing into the tackle area knew it.

Rhythm and tempo were not just part of his passing game, but part of his approach to rugby as a whole – the elements that underpinned his philosophy. He was part of a generation of No 9s, which also included his England successor Richard Hill (with whom I worked closely at Bath), whose passing skills were sufficiently highly developed, and had sufficient variation, to stand up under intense Test-match pressure. Subsequent generations, it seems to me, have produced all-round rugby players who happen to wear the No 9 jersey, rather than "pure" No 9s.

There is no secret to success when it comes to the scrum-half's delivery: it is based on sound technique and sheer hard work of the repetitive variety. People often said Nigel's pass was a thing of beauty and I had no reason to disagree.

Yet for all the talk of technical excellence, the main focus of our chat was centred on the tactical and mental attributes required by a scrum-half hoping to prosper in the higher reaches of the sport. The No 9 is constantly operating under pressure of time, space and physicality. He has the ball in his hands more than anyone else on the field and as a consequence must make more decisions about what happens next. The ability to communicate intelligently in demanding circumstances is vital. As the link between forwards and backs, he must have the capacity to talk to those in front of him while listening to those outside.

Among the many virtues of the top-class scrum-half are organisational capability and the almost indefinable quality of "presence" – things that allow him to remain in control when the going gets tough in confined areas, thereby helping him assess situations and react quickly to them. It is also true that the outstanding No 9s around the world have a high work rate and aerobic capacity: a big engine, if you like. Add the ability to scan on the move and make decisions on the next course of action two or three metres before arriving at the tackle point – eyes-open rugby – and you can see how much is required in maintaining the sense of order and continuity that is so important to the attacking game.

Not every player is blessed with the necessary judgement, the ability to feel the ebb and flow of a game from a position at the heart of the action. To understand the needs of the forwards and adjust things accordingly is a gift (the signals a scrum-half receives are not always as clear as I used to receive from my friend Bill Beaumont, who, during our playing days at Fylde, would say in no uncertain terms: "Kick the bloody thing off the field, Brian, I'm knackered"). Often, the signals are subtler, and interpretation demands a high degree of mental acuity.

To sum up, the scrum-half needs the ability to assess situations – better still, to anticipate them – if he is to steer his colleagues through troubled waters. He must also be cheeky and courageous, an adventurous spirit... even be a little barmy in his approach to life. He is rugby's equivalent of the Test wicketkeeper who somehow finds it within himself to keep encouraging his team-mates and lifting their morale in the last half-hour of a long day in the field. He's the heartbeat, and as such must never allow himself to be subdued or distracted. For him, self-belief is all.

Does anyone in the modern game fit the bill the way Nigel once did? People talk enthusiastically of the French half-back Dimitri Yachvili and I can see why, but he is one on his own – a unique player a long way outside the classical tradition. I have written before of my admiration for the Springbok scrum-half Fourie du Preez, but he is probably past his best. Of today's leading No 9s, I see Will Genia of Australia as a player who fills most of the criteria. As a left-field pick, I was also impressed by Japan's Fumiaki Tanaka at the World Cup.

I have to say, though, that the list in my head is not a long one. Maybe you feel differently.

Wishing Lynagh speedy recovery

Having mentioned Michael Lynagh in connection with the ground-breaking Australian team of 1984, I must also express my deep concern at news that the World Cup-winning outside-half suffered a stroke earlier this week and is under treatment at a hospital in Brisbane. Michael is one of those rare individuals who commands the complete respect of everyone connected with rugby union, to which he continues to make a huge contribution as a broadcaster. Along with the rest of the sporting population, I wish him a strong and speedy recovery.